1. Field of the Invention
The present invention relates generally to data processing systems and, in particular, to a processing system for home terminals that utilizes a single embedded processor and a single random access memory (RAM) for performing not only video/graphics tasks for a wide range of video/graphics standards and modes, but also all functions and controls for a variety of modem, voice algorithm and general purposes operations.
2. Discussion of the Prior Art
A home terminal is a data processing system that is capable of receiving video/graphics data, e.g., text or pictures, from a communications medium, e.g., the telephone lines, processing the received information, and presenting the data in video/graphic form on an output device such as a display monitor or a printer. A home terminal is also capable of sending such data over the communication line to complete the communication link between the home terminal and another system at the other end of the line.
Conventional home terminal systems are typically character generator systems that are based on a combination of dedicated modules: a dedicated modem function that is permanently programmed to receive/transmit only a limited number of modulated signal types, a dedicated video/graphics function that is capable of accommodating only a limited number of video/graphics standards and/or modes, and a general purpose processor or microcontroller that is dedicated to system operation. Furthermore, the general purpose processor and the video/graphics function of these conventional dedicated home terminal architectures each utilize physically separate memory space, thereby increasing operational overhead.
For example, the TS9347 CRT Controller manufactured by SGS Thomson is a character generator video processor that requires a dedicated external RAM for the video functions and a different physical memory space for a separate embedded processor chip. The TS9347 device is also dedicated to a specific terminal type. That is, both the video and processor functions require separate hardware elements which are limited to particular video modes. For example, the TS9347 device cannot be utilized in a BTX system of the type used in Germany or in NAPLPS home terminal implementations in the United States.
The general architecture of a home terminal system that utilizes the TS9347 device, shown in FIG. 1, includes a dedicated modem chip that recovers incoming video/graphics data from the telephone line. A dedicated microcontroller processes the recovered data utilizing code retrieved from an associated read only memory (ROM) to build a corresponding display list which is stored in an associated microcontroller RAM. A dedicated TS9347 controller receives the display list from the microcontroller and utilizes an internal character generator table to generate video output data to an associated monitor.
As stated above, in addition to the limited applications provided by conventional home terminal architectures, because of the need for separate memory space for each of the processing functions, these devices require larger die area and exhibit high system overhead.
Thus, it would be highly desirable to have available a flexible home terminal system that supports a wide range of video standards (e.g., Teletel, Prestel, Ascii, BTX and NAPLPS) and modes (e.g., internal or external color look up tables), a wide range of modems (e.g., V.21, V.22, V.22bis, Be11212, Be11103, V.23, V27ter and V29), and includes flexible voice compression/decompression capability.